1. Field of the Invention
The present invention generally relates to hardcopy apparatus, such as copiers, printers, scanners, and facsimiles, and more particularly to improved media advancing devices for such apparatus.
2. Description of the Prior Art
In hardcopy apparatus and particularly in apparatus handling media of large size, such as large format printers, printed media is outputted from the printer by means of outputting devices that may damage the quality of the printout. Conventional outputting devices, in order to advance the printed media, employ elements for holding the media having direct contact with the printed surface. This may cause markings on the media, ink smearing and other adverse affects on the print appearance.
As an example, the prior art has employed pinch wheels on top of the overdrive roller for outputting printed media. These devices may damage the printout with pinch wheel marks and further require the need to employ a mechanism or a structure to hold the pinch wheels.
To overcome the problem of adverse affects on the print appearance, U.S. Pat. No. 6,234,472 discloses a media holddown device including a vacuum holddown output unit for holding at least a portion of the media down onto a surface of the outputting mechanism. Thus, the device allows holding of the media without direct contact with the printed surface. The vacuum holddown output unit includes a platen having a continuous waved slot that allows for even distribution of a vacuum along the print zone. To advance the media, this device employs a plurality of overdrive wheels with a gap between the overdrive wheels and the surrounding platen. The vacuum is supplied through these gaps and tangentially results in a negative pressure distribution upon the overdrive roller in the area of the outer surface that engages the back of the media. Rotation of the overdrive wheels, that are frictionally engaging a portion of the back of the media due to the negative pressure distribution, advances the media for output. However, the negative pressure distribution of this device provides a limited traction force as a result of the vacuum being tangentially applied to the area of media contact on the overdrive wheels.
Experiments by the present applicant show that such conventional designs behave in such a way that the overdrive wheels begin to act as a friction load for the media advance when the vacuum levels are increased.
The present invention provides an improved media advancing device and method for advancing a printed media in a hardcopy apparatus with increased traction force. The present invention also provides an advancing device that allows for smaller trailing margins.
A media advancing device for a hardcopy apparatus comprising at least one roller having an outer surface and rotatable for advancing media, and a negative pressure mechanism; the outer surface comprising a plurality of openings and a contact region for engaging the media, wherein the negative pressure mechanism is capable of creating negative pressure through at least a portion of the openings in the contact region.
Preferably, the negative pressure mechanism comprises one vacuum source in fluid communication with one vacuum chamber, the vacuum chamber being in fluid communication with at least a portion of said openings in said contact region. More preferably, the vacuum chamber further comprises at least one slot, wherein the at least one roller is partially housed in the at least one slot such that the openings in the contact region provide the only entrance for air through the at least one slot into the vacuum chamber.
The present invention will be described further, by way of example only, with reference to an embodiment thereof as illustrated in the accompanying drawings.